Currently, and in the past, multi-conduit tubulars consisted of either concentric conduits with one inside the other, or integrally joined conduits aligned on the same horizontal plane and covered in an overall jacket of plastic to provide a unitary assembly. One type of integrally joined conduits is available under the trademark name Flatpak™. These items have several inherent limitations in some applications. For example, concentric coil is expensive to manufacture, and difficult to handle. FlatPak™ has temperature limitations due to the external jacket limits and may see premature wear on its external jacket in extreme wellbore conditions and due to equipment problems.
These previous designs were designed to provide methods of deploying and extracting multiple tubular for a variety of purposes, including service and completion work, without the need to hard connect or weld the conduits together. Welding the conduits together is not desirable because the heat affected areas of the continuous tubular do not cycle repeatedly or predictably as the original tubing members are designed for, nor do the heat affected areas resist corrosion as the original tubing members are designed to do.
As in all multiple tubular designs, it is imperative that the tubing members are connected in such a manner that when one tubular wants to move, the other tubular must move, or resist that movement equally, resulting in a product that moves together, even though it consists of many parts. This is especially important when using multiple sizes, and grades of continuous tubing members, because when you continuously deploy these products, the individual tubes will want to stretch, expand, contract, and helix at different rates, and under different conditions. This is why welding the tubes along their vertical line is not recommended, as welding various types of metals together is very tricky. Furthermore, cycling them would become very unpredictable, as the stresses would want to break them apart.
Using conventionally available clamps designed to clamp tubing members together also has inherent flaws. Typically when installed on a continuous coiled tubing member, the clamps are able to slide up and down the coil as they are not directly attached to the coil, and the coil can be slightly undersized at times from the manufacturer, or it can see reduced O.D. from stretch, working (cycling), or from temperature changes. Whenever a size change occurs, the clamps could slip, resulting in large sections of the overall package with no clamps at all, allowing the individual strings to “bow” or “flex” at will, and possibly resulting in a large number of clamps all stacked up in one spot. Known clamp designs are also generally unable to be spooled and thus are required to be installed as the tubing is injected into the wellbore.
U.S. Pat. No. 5,379,836 by Jordan discloses a clamp for use with a well tubular, and more particularly to a clamp for joining auxiliary electrical lines alongside a wellbore tubing member. The clamp relies on being clamped overtop of joint in discontinuous jointed tubing in order to prevent sliding misplacement of the clamp along tubing member. Without the interlocking connection of the clamp body about axially opposed ends of an enlarged connection in the jointed tubing, the clamp design is not suited to remaining fixed in position along the tubing member and thus is unsuitable for use with continuous coiled tubing members. Furthermore, the clamp cannot be spooled as it must be installed on the jointed tubing as the tubing is joined prior to insertion into a wellbore.
WO 2013/134868 by Morris, filed Mar. 5, 2013 discloses a coiled tubing assembly for use in a wellbore which includes at least two continuous coiled tubing members which are joined by clamp assemblies at longitudinally spaced positions. Each clamp assembly has a central portion spanning between the spaced apart coiled tubing members and clamping portions joined to the central portion to extend about the tubing members respectively. Each clamping portion is maintained in an elastically stretched state in a circumferential direction about the respective tubing member such that the internal circumference of the clamping portion is arranged to be elastically reduced about the respective tubing member when the tubing member stretches longitudinally in use within a wellbore. Use of tension by the elastic stretching of the clamping portions about the tubing members alone however may be insufficient to hold the longitudinal position of the clamping members in some instances. Welding one or more clamping portions to the respective tubular member is sufficient to maintain the longitudinal position of the clamping members in some instances. In longer runs of tubing members however, the relative twisting of the coiled tubing members resulting from unspooling may result in breakage of the longitudinal positioning welds such that the clamps are again unable to be held in the longitudinal direction along the tubular members.